Picosecond laser apparatus and methods for its operation and use
View Patent ↗Apparatuses and methods are disclosed for applying laser energy having desired pulse characteristics, including a sufficiently short duration and/or a sufficiently high energy for the photomechanical treatment of skin pigmentations and pigmented lesions, both naturally-occurring (e.g., birthmarks), as well as artificial (e.g., tattoos). The laser energy may be generated with an apparatus having a resonator with the capability of switching between a modelocked pulse operating mode and an amplification operating mode. The operating modes are carried out through the application of a time-dependent bias voltage, having waveforms as described herein, to an electro-optical device (e.g., a Pockels cell) positioned along the optical axis of the resonator.
1. A method for treating a skin pigmentation, the method comprising generating pulsed laser energy by
a) reflecting laser energy generated by a lasing medium between a first mirror at one end of a resonator and a second mirror at the opposite end of said resonator and through a polarizer and one or additional electro-optical devices within said resonator and generating a modelocked pulse within the resonator by applying a periodic voltage waveform to the one or additional electro-optical devices; and
(b) then amplifying the modelocked pulse by applying to said one or additional electro-optical devices a first constant voltage and maintaining an effective reflectivity of the second mirror at substantially 100%; and
(c) then extracting the amplified modelocked pulse from the resonator, and exposing pigmented skin of a patient to the pulsed laser energy.
2. The method of claim 1 wherein the amplified modelocked pulse is extracted from the resonator by applying a second constant voltage to said one or additional electro-optical devices and maintaining an effective reflectivity of the second mirror at substantially 0%.
3. The method of claim 1 , wherein the periodic voltage waveform is equal to the sum of a baseline voltage, V o , and a time-dependent differential voltage, δV(t), that varies periodically with a period substantially equal to the twice the time required for said laser energy to traverse the length of said resonator said baseline voltage V o is from about 30% to about 70% of the quarter wave voltage of said one or additional electro-optical devices.
4. The method of claim 3 , wherein said baseline voltage V o is from about 40% to about 60% of the quarter wave voltage of said one or additional electro-optical devices.
5. The method of claim 3 , wherein said time-dependent differential voltage, δV(t), has an amplitude from about 5% to about 35% of the quarter wave voltage of said one or additional electro-optical devices.
6. The method of claim 3 , wherein said time-dependent differential voltage, δV(t), has an amplitude from about 10% to about 30% of the quarter wave voltage of said one or additional electro-optical devices.
7. The method of claim 1 , wherein said one or additional electro-optical devices is a Pockels cell.
8. The method of claim 2 , wherein said first constant voltage is substantially 0 and said second constant voltage is substantially equal to the quarter wave voltage of said one or additional electro-optical devices.
9. The method of claim 1 , wherein said pulsed laser energy has from about 200 to about 800 mj/pulse.
10. The method of claim 1 , wherein said pulsed laser energy has a pulse duration of at most about 150 ps.
11. The method of claim 1 , wherein said skin pigmentation is a tattoo or a birthmark.
12. A method for removing a tattoo comprising tattoo pigment particles, the method comprising exposing said tattoo pigment particles to pulsed laser energy with pulses having a duration below about twice the acoustic transit time across said tattoo pigment particles.
13. The method of claim 12 , wherein said tattoo particles have a diameter from about 1 to about 10 microns.
14. The method of claim 12 , wherein said pulses have an energy of at least about 100 mj.
15. The method of claim 12 , wherein said duration is at most about 500 ps.
16. The method of claim 1 wherein the pulsed laser energy includes pulses having a duration of at most about 500 ps.
17. The method of claim 1 wherein the pulsed laser energy includes an energy of at least about 100 mj/pulse.
18. The method of claim 1 wherein the pulsed laser energy includes pulses having a duration of less than about 1 nanosecond.
19. The method of claim 1 wherein the pulsed laser energy includes pulses having a duration of less than about 500 ps.
20. The method of claim 1 wherein the pulsed laser energy includes pulses having a duration of between about 100 ps and about 300 ps.
21. The method of claim 1 , wherein said skin pigmentation is a pigmented lesion.
22. The method of claim 12 comprising exposing said tattoo pigment particles to pulsed laser energy with pulses having a duration below about five times the acoustic transit time across said tattoo pigment particles.
23. A method for removing a skin pigmentation comprising pigment particles, the method comprising exposing said pigment particles to pulsed laser energy with pulses having a duration below about twice the acoustic transit time across said pigment particles.
24. The method of claim 23 comprising exposing said pigment particles to pulsed laser energy with pulses having a duration below about five times the acoustic transit time across said pigment particles.
25. The method of claim 23 , wherein said particles have a diameter from about 1 to about 10 microns.
26. The method of claim 23 , wherein said pulses have an energy of at least about 100 mj.
27. The method of claim 23 , wherein said duration is at most about 500 ps.